The present invention relates to optical measuring systems and methods, and more particularly to nondestructive optical systems and methods for simultaneously measuring optical constants (n, k) and thickness of thin films.
There are several known methods for determining the optical constants and thickness of thin films. One conventional method is disclosed in “Handbook of Optical Constants of Solids”, edited by E. D. Palik (academic Press, N.Y., 1985). This method measures normal-incidence reflectance and transmittance over a wide spectral range.
Another conventional method is disclosed in “Handbook of Optical Constants of Solids II”, edited by E. D. Palik (Academic Press, N.Y., 1991). This method measures R and T for normal and oblique angles of incidence (45′; 60′) for the polarizations TE and TM, over a wide spectral range.
Another conventional method is disclosed by O. S. Heavens in “Physics of Thin Films”, Vol. 2, edited by G. Hass and R. E. Thum (Academic Press, N.Y., 1964). This method uses ellipsometry to measurement the polarization states of collimated monochromatic light before and after reflection from a surface to obtain the ratio ρ=rp/rS,=tan ψ exp(i Δ) of the complex p and s reflection coefficients.
However, for very thin films (on the order of a few atomic layers), these methods are not capable of measuring the optical constants (n and k) and thickness independently, and at times yield inaccurate results. A major disadvantage of these conventional methods is that the optical constants and thickness are coupled and for very thin films they cannot be decoupled or measured independently.
Accordingly, it would be advantageous to have systems and methods for measuring the thickness and optical constants of very thin films independently.